The present invention relates generally to optical instruments for measuring refractive index of a substance, and, more particularly, to an optical configuration and method for measuring a difference in refractive index between at least one test sample and a reference sample. The present invention is applicable to surface plasmon resonance (SPR) applications. Biosensors are measured with the use of SPR as well.
The phenomenon of surface plasmon resonance, or SPR, is well known. SPR causes a drop in the intensity of light reflected from the interface of an optically transparent substance and a metal surface at a specific wavelength and angle of incidence. The location of the intensity minimum, measured with respect to wavelength of the incident light or the angle of incidence of the light with respect to the metal surface, changes when differing compositions of substances are placed in a sample space on the metal surface opposite the transparent substance. By measuring the location of the intensity minimum, the identity of the substance in contact with the metal surface may be determined.
Devices have been developed to use SPR in making optical measurements. More specifically, U.S. Pat. No. 5,313,264 to Ivarsson et al. describes an optical biosensor system that comprises a plurality of side-by-side sensing surfaces 39A-D illuminated by a streak of light 5 extending transversely across the sensing surfaces, and an anamorphic lens system 6 by which rays of light reflected from the respective sensing surfaces are imaged on corresponding columns of a two-dimensional array 7 of photosensitive elements. Accordingly, the signals from the photosensitive elements can be processed to determine a minimum reflectance associated with the resonance angle at each sensing surface. Although the system described in U.S. Pat. No. 5,313,264 avoids the use of moving parts, it is nevertheless optically complex and requires a two-dimensional array, factors that are accompanied by an increase in cost.
Finally, it is noted that one-dimensional (linear) arrays of photosensitive elements cells are commonly used in automatic refractometers designed to take non-differential readings with respect to a single test sample. Examples can be found in U.S. Pat. No. 4,640,616 (Michalik) and U.S. Pat. No. 6,172,746 (Byrne et al.). However, the patentee is unaware of any SPR measurement device that analyzes two samples simultaneously using a linear array, despite the recognized economy offered by this type of array.
Clearly, then, there is a longfelt need for an apparatus that can multiplex two SPR channels onto a single one-dimensional array.
The invention broadly comprises an apparatus for performing optical measurements having a light source operatively arranged to emit light along a beam path, a prism, a sensor chip mounted to a sample surface of the prism, and a detector operatively arranged to measure intensity of light reflected from the intermittent members of the metallic film. The sensor chip has a metallic film with a plurality of intermittent members, a first sample reservoir, and a second sample reservoir. The first and second reservoirs are operatively arranged to hold and position a sample on at least one member of a plurality of intermittent members of the metallic film.
The invention also broadly comprises a sensor chip for an optical instrument comprising a transparent member, a first and a second light reflective member, and a first and a second reservoir. The first light reflective member has a portion offset from the second light reflective member in a direction parallel to a meridional plane of the optical instrument. The second light reflective member has a portion offset from the first light reflective member in a direction parallel to the meridional plane of the optical instrument. The first reservoir is located above the first light reflective member and the second reservoir is located above the second light reflective member.
The invention also comprises a device for reflecting light in an optical instrument comprising at least two reservoirs located on a metallic film having a plurality of intermittent members operatively arranged to define at least two regions on a detector. Each of the at least two regions comprises light reflected from a member in communication with only one of the reservoirs.
Finally, the invention provides a method for performing optical measurements comprising the steps of directing a beam of light from a light source through a first face of a prism, reflecting a portion of the directed beam of light from a second face of the prism, and detecting the reflected light with a detector. The second face of the prism has a first and a second reservoir, each holding one of the two samples. The first reservoir is located above a first light reflective member and the second reservoir is located above a second light reflective member. The first light reflective member has a portion offset from the second light reflective member in a direction parallel to the meridional plane of the apparatus. The second light reflective member has a portion offset from the first light reflective member in a direction parallel to the meridional plane of the apparatus.
A general object of the present invention is to provide an apparatus for multiplexing two SPR channels onto a single linear scanned array.
These and other objects, features and advantages of the present invention will become readily apparent to those having ordinary skill in the art upon a reading of the following detailed description of the invention in view of the drawings and claims.